A typical wireless communication system comprises a plurality of wireless communications devices exchanging data with each other. In some wireless communication systems, for example, infrastructure networks, the system may further comprise a wireless base station for managing communications between the wireless communications devices. In other words, each intra-system communication would be exchanged via the wireless base station. In other wireless communication systems, for example, mesh networks and ad hoc wireless networks, the wireless base station may be omitted, i.e. the wireless communications devices may communicate directly with each other.
A typical Extremely High Frequency (EHF), i.e. 30 to 300 GHz, communication system operating at this band may have some drawbacks. For example, transmission of the signals over coaxial cable may incur large attenuation effects. Moreover, in applications where RF devices are used, the size, weight, and power (SWaP) of the components may increase to undesirable levels. Moreover, downstream receiver processing, such as downconverting, and signal addressing may be difficult.
One approach to these drawbacks in EHF communication systems may comprise the use of optical components for processing components. An advantage of such systems is the ability to transmit EHF signals from a remote location without the degradation of the signal incumbent in RF applications.
For example, as disclosed in U.S. Pat. No. 5,710,651 to Logan, Jr., an EHF communication system comprises a remote antenna station, a transmitter/receiver station, and an optical fiber coupling the stations together. These stations comprise photodiodes for converting the transmitted optical signal to an electrical signal, and lasers paired with optical modulators for converting the received EHF signal to an optical signal.
Nevertheless, optical applications such as this may be subject to certain drawbacks. For example, the systems may be subject to chromatic dispersion-induced signal fading. In particular, optical heterodyne approaches may be limited by phase noise of laser sources.
U.S. Patent Application Publication No. 2013/0236187 to Middleton et al., also assigned to present application's assignee, the contents of which are hereby incorporated by reference in their entirety, discloses in FIG. 1 a communications device 120 comprising a transmitter device 121 comprising an optical source 122 generating an optical carrier signal, a first electro-optic (E/O) modulator 123 coupled to the optical source and modulating the optical carrier signal with an input signal having a first frequency, and a second E/O modulator 124 coupled to the optical source and modulating the optical carrier signal with a reference signal. The communications device 120 includes a receiver device 125, and an optical waveguide 129 coupled between the transmitter 121 and receiver devices.
The transmitter device 121 includes a first band pass filter 133 coupled downstream from the first E/O modulator 123 and passing (i.e. selecting and rejecting everything else) a carrier frequency sideband, and a second band pass filter 134 coupled downstream from the second E/O modulator 124 and passing a reference signal frequency sideband. The first and second band pass filters 133-134 each comprises a fiber Bragg grating 149, 151 and an associated circulator 148, 152.
The receiver device 125 comprises an optic-electro (O/E) converter 126 including first and second optical detectors 146a-146b coupled to the optical waveguide 129, and a combiner 147 coupled to the first and second optical detectors. The transmitter device comprises an amplifier 127 coupled between the optical source 122 and the first and second E/O modulators 123-124.
Additionally, the transmitter device 121 further comprises an optical splitter 128 coupled between the optical source 122 and the first and second E/O modulators 123-124, and an RF input block 132, such as antenna, coupled to the first E/O modulator. The transmitter device 121 also includes a local oscillator (LO) 131 for generating the reference signal, and a directional coupler 135 coupled between said first and second band pass filters 133-134 and the O/E converter 126. The LO 131 is adjusted to control the frequency conversion of the output signal.